1 comment:

Jim Hansen, Roy Spencer (and IPCC et al) are all wrong in assuming the atmosphere would be isothermal without GHG.

They are also wrong in assuming that the Sun was capable of warming the surface of Venus, Earth or other planets to the observed temperature which is then maintained by back radiation being supposedly the only process that slows such surface cooling. They forgot that conduction and evaporation also decrease with a narrowing temperature gap.

The Second Law of Thermodynamics is stated (in Wikipedia “Laws of Thermodynamics”) thus …

“An isolated system, if not already in its state of thermodynamic equilibrium, spontaneously evolves towards it. Thermodynamic equilibrium has the greatest entropy amongst the states accessible to the system.”

If there were to be a sealed cylinder of air which was isothermal, then there would be an “ordered” state with more total energy (PE + KE) at the top. Hence this would not be an equilibrium state, because entropy could increase, and it must. There will only be equilibrium when the sum (PE+KE) is the same at all heights.

A vertical isothermal state in a gravitational field has less entropy than an isentropic state, the latter having maximum possible entropy, and thus being the equilibrium state as referred to in the Second Law of Thermodynamics as I quoted it above from the Wikipedia “Laws of Thermodynamics’ item. Hence a thermal gradient forms autonomously by diffusion at the molecular level.

Furthermore, any additional thermal energy deposited at the top can, and will, diffuse towards the bottom, creating a new equilibrium. This means there can be a heat transfer up the thermal gradient if that gradient is equal to or less in absolute magnitude than the normal equilibrium thermal gradient.

This is how energy absorbed in the Venus (or Earth) atmosphere at any altitude from any source, be it upwelling or downwelling radiation or latent heat release (on Earth) can flow towards the surface, heating the base of the atmosphere and subsequently heating the surface, or “supporting” its existing slightly warmer temperature by slowing the rate of cooling.